1. Field of the Invention
The present invention relates to a technique that creates dots on a printing medium, so as to print a variety of images. More specifically the invention pertains to a technique that controls creation of dots on the contour of an image, so as to enhance the picture quality of the resulting image.
2. Description of the Related Art
Printing apparatuses that create ink dots on a printing medium to print an image are widely used as output devices of various images output from the computer, for example, natural images, letters, and figures. The printing apparatus divides an image into fine pixels and creates dots on the printing medium according to the tone values of the respective pixels, thereby printing the image. The technique applied for the printing apparatus determines creation or non-creation of a dot with regard to each pixel according to its tone value, in such a manner that dots are formed at a higher ratio in dark areas (where pixels have high tone values) of the printed image but formed at a lower ratio in light areas (where pixels having low tone values) of the printed image. The dots are created at the corresponding pixel positions, based on the results of the determination. The resulting printed image has a variation in brightness according to the density of dots and thus attains a wide range of tone value expression.
In the dark areas of the printed image, the control procedure determines creation of dots at a higher density. Namely dots are formed in most pixel positions in these areas. When the dots created there have a relatively small size, there is often a streak of clearance on the boundary between pixels, which is generally called banding and worsens the picture quality. The size of the dots formed on the printing medium is accordingly regulated to be greater than the interval between pixels.
Some proposed printers actively regulate the size of dots formed on the printing medium. In the case where the size of dots is not regulated, there are only two expressible levels, that is, creation or non-creation of the dot, in the respective pixels. In the case where the size of dots is regulated, on the other hand, there are a greater number of expressible levels in each pixel, which ensures the richer tone expression. The proposed technique allocates the larger-size dot to the pixels having high tone values and the smaller-size dot to the pixels having low tone values. Compared with the conventional technique that simply expresses the tone according to the density of dots, this proposed technique expands the degree of freedom in tone expression and enables a natural image having a wide range of tone values to be printed with a high quality.
These prior art printers, however, have a problem that the contour of a figure or a letter may be thickened in print. The figures and letters are generally expressed in black and have high tone values. The larger-size dot is accordingly allocated to such figures and letters. Since the size of the large dot is designed to be greater than the pixel, the printed contour is made thicker than expected. Allocation of the smaller-size dot to the contour may, however, cause the banding.
In these prior art printers, the printed figure or letter may have a relatively rough contour, which lowers the picture quality of the printed image. The dots are formed in the respective pixel positions, which are obtained by dividing the image as mentioned above. Unless the contour line coincides with the direction of alignment of pixels, the contour should be approximated by a broken line, which may result in a relatively rough contour. Increasing the number of divisions of the image to make the respective pixels smaller ensures the smooth contour. The time period required for printing the image, however, increases with an increase in number of pixels constituting the image.
The object of the present invention is thus to provide a technique that improves the picture quality of a printed image including figures or letters.
At least part of the above and the other related objects is actualized by a first printer having a print head that enables creation of at least two variable-size dots, that is, a larger-size dot and a smaller-size dot. The first printer drives the print head and carries out both main scan and sub-scan to print an image. The first printer includes: a contour pixel extraction unit that extracts contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; a dot creation decision unit that determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocates the smaller-size dot to each of the contour pixels extracted by the contour pixel extraction unit; and a dot creation unit that actually creates the at least two variable-size dots, based on results of the determination and the allocation with regard to the respective pixels by the dot creation decision unit.
The present invention is also directed to a first method of printing that corresponds to the first printer. The invention accordingly provides the first method of driving a print head and carrying out both main scan and sub-scan to print an image, wherein the print head enables creation of at least two variable-size dots, that is, a larger-size dot and a smaller-size dot. The first method includes the steps of: (a) extracting contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; (b) determining creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocating the smaller-size dot to each of the contour pixels extracted in the step (a); and (c) actually creating the at least two variable-size dots, based on results of the determination and the allocation with regard to the respective pixels in the step (b).
In the first printer and the corresponding first method, the technique of the present invention extracts contour pixels included in the image, determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and allocates the smaller-size dot to the extracted contour pixels. The at least two variable-size dots are formed according to the result of the determination with regard to the respective pixels. The smaller-size dot is allocated to the contour of a shape included in the image. This arrangement effectively prevents the contour from being undesirably thickened and thereby improves the picture quality of a resulting printed image.
The smaller-size dot is formed in the respective contour pixels, whereas the larger-size dot is created inside the shape. For example, in the case of printing black letters or figure, the larger-size dot is allocated to the inside of the respective letters or figure. This enables the contour of the shape to be printed clearly in deep black and effectively prevents banding from occurring even in solid areas of the figure.
In the first printer and the corresponding first method, one preferable application of the technique defines a plurality of adjoining pixels in a main scanning direction as one set, compares a tone value of each pixel included in the set with a predetermined threshold value, and extracts the contour pixels based on a result of the comparison and a preset relationship. The extraction of contour pixels according to this procedure desirably improves the picture quality of the resulting printed image.
In the first printer and the corresponding first method, another preferable application of the technique tentatively determines creation or non-creation of each of the at least two variable-size dots in each pixel based on the image data, stores a result of the tentative determination, rewrites the result of the tentative determination to create the smaller-size dot in the contour pixels, and settles the rewritten result as a result of the determination by the dot creation decision unit. The at least two variable-size dots are formed according to the result of the determination thus obtained, and the smaller-size dot is formed in the respective contour pixels. This arrangement favorably improves the picture quality of the resulting printed image.
At least part of the above and the other related objects is also actualized by a second printer having a print head that enables creation of at least two variable-size dots. The second printer drives the print head and carries out both main scan and sub-scan to print an image. The second printer includes: a resolution reduction unit that collects a plurality of adjoining pixels among all the pixels constituting the image into one large pixel based on a predetermined relationship, and expresses the image with the large pixels; a contour pixel extraction unit that extracts contour large pixels based on image data, the contour large pixels representing the contour of a shape included in the image; a dot creation decision unit that determines creation or non-creation of each of the at least two variable-size dots with regard to each large pixel based on the image data, and selects one of the at least two variable-size dots, which is to be created in each of the extracted contour large pixels, based on the image data with regard to the plurality of adjoining pixels collected into the contour large pixel; and a dot creation unit that actually creates the at least two variable-size dots, based on results of the determination and the selection with regard to the respective large pixels by the dot creation decision unit.
The present invention is further directed to a second method of printing that corresponds to the second printer. The invention accordingly provides the second method of driving a print head and carrying out both main scan and sub-scan to print an image, wherein the print head enables creation of at least two variable-size dots. The second method includes the steps of: (a) collecting a plurality of adjoining pixels among all the pixels constituting the image into one large pixel based on a predetermined relationship, and expressing the image with the large pixels; (b) extracting contour large pixels based on image data, the contour large pixels representing the contour of a shape included in the image; (c) determining creation or non-creation of each of the at least two variable-size dots with regard to each large pixel based on the image data, and selecting one of the at least two variable-size dots, which is to be created in each of the extracted contour large pixels, based on the image data with regard to the plurality of adjoining pixels collected into the contour large pixel; and (d) actually creating the at least two variable-size dots, based on results of the determination and the selection with regard to the respective large pixels in the step (c).
In the second printer and the corresponding second method, the technique of the present invention collects a plurality of adjoining pixels among all the pixels constituting the image into one large pixel based on a predetermined relationship, expresses the image with the large pixels, and extracts contour large pixels from the large pixels constituting the image. The technique subsequently determines the dot to be created in each large pixel based on image data, and selects one of the at least two variable-size dots, which is to be created in each of the extracted contour large pixels, based on the image data with regard to the plurality of adjoining pixels collected into the contour large pixel. The respective dots are then formed according to the results of the determination and the selection obtained for the respective large pixels. This arrangement enables the contour of a shape included in the image to be printed with adequate dots, on which information on the plurality of adjoining pixels collected to each large pixel is reflected. This gives a smooth contour and improves the printing quality.
The technique of the second printer and the corresponding second method prints the large pixels constituting the contour with adequate-size dots, while not increasing the number of dots required for printing the image. This arrangement thus ensures the high-quality printing without increasing the time period required for printing.
In accordance with one preferable application of the second printer and the corresponding second method, a position of creating a predetermined-size dot among the at least two variable-size dots is shifted in a preset direction from a position of creating another dot among the at least two variable-size dots. The preferable application of the technique analyzes a tone value distribution of the plurality of adjoining pixels collected into each contour large pixel, and determines that the predetermined-size dot is to be created in the contour large pixel when the tone value distribution is deviated in a direction substantially identical with the preset direction. The respective dots are created according to the results of the determination. This arrangement enables the dots to be formed at desirable positions and constitute the contour of the printed image. This gives a smoother contour and improves the printing quality. This arrangement of the printer and the method also prints the large pixels constituting the contour included in the printed image with adequate-size dots, while not increasing the number of dots required for printing the image. This arrangement thus ensures the high-quality printing without increasing the time period required for printing.
In accordance with another preferable application of the second printer and the corresponding second method, a position of creating a predetermined-size dot among the at least two variable-size dots is shifted in the main scanning direction from a position of creating another dot among the at least two variable-size dots. The preferable application of the technique analyzes a tone value distribution of the plurality of adjoining pixels collected into each contour large pixel, and determines that the predetermined-size dot is to be created in the contour large pixel when the tone value distribution is deviated in a direction substantially identical with the main scanning direction. This arrangement enables the dots to be formed at desirable positions and constitute the contour of the printed image. This gives a smoother contour and improves the printing quality.
In the second printer and the corresponding second method, one preferable application of the technique tentatively determines creation or non-creation of each of the at least two variable-size dots in each large pixel based on the image data, stores a result of the tentative determination, selects one of the at least two variable-size dots, which is to be created in each contour large pixel, based on the image data with regard to the plurality of adjoining pixels collected into the contour large pixel, rewrites the result of the tentative determination in order to create the selected dot in each contour large pixel, and settles the rewritten result as a result of the determination by the dot creation decision unit. The respective dots are formed according to the results of the determination and the selection thus obtained. This arrangement enables adequate dots, on which information on the plurality of adjoining pixels collected to each large pixel is reflected, to be created in the contour pixels. This gives a smooth contour and improves the printing quality.
At least part of the above and the other related objects is also actualized by a third printer having a print head that enables creation of at least two variable-size dots. The third printer drives the print head and carries out both main scan and sub-scan to print an image. The third printer includes: a contour pixel extraction unit that extracts contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; a dot creation decision unit that determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, the dot creation decision unit dividing each of the contour pixels into a plurality of adjoining small pixels and selecting one of the at least two variable-size dots, which is to be created in each of the contour pixels, based on tone values of the respective small pixels that are specified according to a predetermined relationship; and a dot creation unit that actually creates the at least two variable-size dots, based on results of the determination and the selection with regard to the respective pixels by the dot creation decision unit.
The present invention is also directed to a third method of printing that corresponds to the third printer. The invention accordingly provides the third method of driving a print head and carrying out both main scan and sub-scan to print an image, wherein the print head enables creation of at least two variable-size dots. The third method includes the steps of: (a) extracting contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; (b) determining creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, dividing each of the contour pixels into a plurality of adjoining small pixels, and selecting one of the at least two variable-size dots, which is to be created in each of the contour pixels, based on tone values of the respective small pixels that are specified according to a predetermined relationship; and (c) actually creating the at least two variable-size dots, based on results of the determination and the selection with regard to the respective pixels in the step (b).
In the third printer and the corresponding third method, the technique of the present invention extracts contour pixels based on image data, determines creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, divides each of the contour pixels into a plurality of adjoining small pixels, and selects one of the at least two variable-size dots, which is to be created in each of the contour pixels, based on tone values of the respective small pixels that are specified according to a predetermined relationship. The respective dots are formed on a printing medium according to the results of the determination and the selection thus obtained. This arrangement enables adequate dots, on which information on the adjoining small pixels is reflected, to be created on the contour. This gives a smoother contour and improves the printing quality.
The technique of the third printer and the corresponding third method prints the pixels constituting the contour with adequate-size dots, while not increasing the number of dots required for printing the image. This arrangement thus ensures the high-quality printing without increasing the time period required for printing.
In accordance with one preferable application of the third printer and the corresponding third method, a position of creating a predetermined-size dot among the at least two variable-size dots is shifted in a preset direction from a position of creating another dot among the at least two variable-size dots. The preferable application of the technique analyzes a tone value distribution with regard to the plurality of adjoining small pixels, which are obtained by dividing each contour pixel, and determines that the predetermined-size dot is to be created in the contour pixel when the tone value distribution is deviated in a direction substantially identical with the preset direction. This arrangement enables the dots to be formed at desirable positions and constitute the contour of the printed image. This gives a smoother contour and improves the printing quality. This arrangement of the printer and the method does not increase the number of dots required for printing the image. This arrangement thus ensures the high-quality printing without increasing the time period required for printing.
In accordance with another preferable application of the third printer and the corresponding third method, a position of creating a predetermined-size dot among the at least two variable-size dots is shifted in a main scanning direction from a position of creating another dot among the at least two variable-size dots. The preferable application of the technique analyzes a tone value distribution with regard to the plurality of adjoining small pixels, which are obtained by dividing each contour pixel in the main scanning direction, and determines that the predetermined-size dot is to be created in the contour pixel when the tone value distribution is deviated in a direction substantially identical with the main scanning direction. This arrangement enables the dots to be formed at desirable positions and constitute the contour of the printed image. This gives a smoother contour and improves the printing quality.
In the third printer and the corresponding third method, one preferable application of the technique tentatively determines creation or non-creation of each of the at least two variable-size dots in each pixel based on the image data, stores a result of the tentative determination, selects one of the at least two variable-size dots, which is to be created in each contour pixel, based on the tone values of the respective small pixels that are specified according to the predetermined relationship, rewrites the result of the tentative determination in order to create the selected dot in each contour pixel, and settles the rewritten result as a result of the determination by the dot creation decision unit. The respective dots are formed according to the results of the determination and the selection thus obtained. This arrangement enables adequate dots, on which information on the adjoining small pixels is reflected, to be created on the contour. This gives a smoother contour and improves the printing quality.
The first through the third methods discussed above may be actualized under the control of a computer included in a printing apparatus that utilizes a print head enabling creation of at least two variable-size dots. Another possible application of the present invention is thus a recording medium, on which a program for actualizing the respective functions discussed above is recorded in a computer readable manner.
The present invention is directed to a first recording medium, which corresponds to the first printer and the first method discussed above. The invention accordingly provides the first recording medium, on which a program is recorded in a computer readable manner. The program is used in a printer that enables creation of at least two variable-size dots, that is, a larger-size dot and a smaller-size dot. The program is activated to carry out a predetermined operation for image data representing the image, in order to determine creation or non-creation of each of the at least two variable-size dots with regard to each pixel. The program includes: a program code that causes a computer to extract contour pixels based on the image data, the contour pixels representing the contour of a shape included in the image; and a program code that causes the computer to determine creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, and to allocate the smaller-size dot to each of the contour pixels.
The present invention is further directed to a second recording medium, which corresponds to the second printer and the second method discussed above. The invention accordingly provides the second recording medium, on which a program is recorded in a computer readable manner. The program is used in a printer that enables creation of at least two variable-size dots. The program is activated to carry out a predetermined operation for image data representing the image, in order to determine creation or non-creation of each of the at least two variable-size dots with regard to each pixel. The program includes: a program code that causes a computer to collect a plurality of adjoining pixels among all the pixels constituting the image into one large pixel based on a predetermined relationship, and to express the image with the large pixels; a program code that causes the computer to extract contour large pixels based on image data, the contour large pixels representing the contour of a shape included in the image; and a program code that causes the computer to determine creation or non-creation of each of the at least two variable-size dots with regard to each large pixel based on the image data, and to select one of the at least two variable-size dots, which is to be created in each of the extracted contour large pixels, based on the image data with regard to the plurality of adjoining pixels collected into the contour large pixel.
The present invention is also directed to a third recording medium, which corresponds to the third printer and the third method discussed above. The invention accordingly provides the third recording medium, on which a program is recorded in a computer readable manner. The program is used in a printer that enables creation of at least two variable-size dots. The program is activated to carry out a predetermined operation for image data representing the image, in order to determine creation or non-creation of each of the at least two variable-size dots with regard to each pixel. The program includes: a program code that causes a computer to extract contour pixels based on image data, the contour pixels representing the contour of a shape included in the image; and a program code that causes the computer to determine creation or non-creation of each of the at least two variable-size dots with regard to each pixel based on the image data, to divide each of the contour pixels into a plurality of adjoining small pixels, and to select one of the at least two variable-size dots, which is to be created in each of the contour pixels, based on tone values of the respective small pixels that are specified according to a predetermined relationship.
The computer reads the program recorded on one of the first through the third recording media and controls the printer, thereby improving the picture quality on the contour of the resulting printed image.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment with the accompanying drawings.